[OPENMP] What's new for OpenMP in clang.

Updated ReleaseNotes + Status of the OpenMP support in clang.

llvm-svn: 338049

1 files changed, 69 insertions, 6 deletions

diff --git a/clang/docs/OpenMPSupport.rst b/clang/docs/OpenMPSupport.rst
index f34049473f8..e8ec1e371b0 100644
--- a/clang/docs/OpenMPSupport.rst
+++ b/clang/docs/OpenMPSupport.rst
@@ -10,13 +10,15 @@
 .. role:: partial
 .. role:: good
 
+.. contents::
+   :local:
+
 ==================
 OpenMP Support
 ==================
 
-Clang fully supports OpenMP 3.1 + some elements of OpenMP 4.5. Clang supports offloading to X86_64, AArch64 and PPC64[LE] devices.
-Support for Cuda devices is not ready yet.
-The status of major OpenMP 4.5 features support in Clang.
+Clang fully supports OpenMP 4.5. Clang supports offloading to X86_64, AArch64,
+PPC64[LE] and has `basic support for Cuda devices`_.
 
 Standalone directives
 =====================
@@ -35,7 +37,7 @@ Standalone directives
 
 * #pragma omp target: :good:`Complete`.
 
-* #pragma omp declare target: :partial:`Partial`.  No full codegen support.
+* #pragma omp declare target: :good:`Complete`.
 
 * #pragma omp teams: :good:`Complete`.
 
@@ -64,5 +66,66 @@ Combined directives
 
 * #pragma omp target teams distribute parallel for [simd]: :good:`Complete`.
 
-Clang does not support any constructs/updates from upcoming OpenMP 5.0 except for `reduction`-based clauses in the `task` and `target`-based directives.
-In addition, the LLVM OpenMP runtime `libomp` supports the OpenMP Tools Interface (OMPT) on x86, x86_64, AArch64, and PPC64 on Linux, Windows, and mac OS.
+Clang does not support any constructs/updates from upcoming OpenMP 5.0 except
+for `reduction`-based clauses in the `task` and `target`-based directives.
+
+In addition, the LLVM OpenMP runtime `libomp` supports the OpenMP Tools
+Interface (OMPT) on x86, x86_64, AArch64, and PPC64 on Linux, Windows, and mac OS.
+ows, and mac OS.
+
+.. _basic support for Cuda devices:
+
+Cuda devices support
+====================
+
+Directives execution modes
+--------------------------
+
+Clang code generation for target regions supports two modes: the SPMD and
+non-SPMD modes. Clang chooses one of these two modes automatically based on the
+way directives and clauses on those directives are used. The SPMD mode uses a
+simplified set of runtime functions thus increasing performance at the cost of
+supporting some OpenMP features. The non-SPMD mode is the most generic mode and
+supports all currently available OpenMP features. The compiler will always
+attempt to use the SPMD mode wherever possible. SPMD mode will not be used if:
+
+   - The target region contains an `if()` clause that refers to a `parallel`
+     directive.
+
+   - The target region contains a `parallel` directive with a `num_threads()`
+     clause.
+
+   - The target region contains user code (other than OpenMP-specific
+     directives) in between the `target` and the `parallel` directives.
+
+Data-sharing modes
+------------------
+
+Clang supports two data-sharing models for Cuda devices: `Generic` and `Cuda`
+modes. The default mode is `Generic`. `Cuda` mode can give an additional
+performance and can be activated using the `-fopenmp-cuda-mode` flag. In
+`Generic` mode all local variables that can be shared in the parallel regions
+are stored in the global memory. In `Cuda` mode local variables are not shared
+between the threads and it is user responsibility to share the required data
+between the threads in the parallel regions.
+
+Features not supported or with limited support for Cuda devices
+---------------------------------------------------------------
+
+- Reductions across the teams are not supported yet.
+
+- Cancellation constructs are not supported.
+
+- Doacross loop nest is not supported.
+
+- User-defined reductions are supported only for trivial types.
+
+- Nested parallelism: inner parallel regions are executed sequentially.
+
+- Static linking of libraries containing device code is not supported yet.
+
+- Automatic translation of math functions in target regions to device-specific
+  math functions is not implemented yet.
+
+- Debug information for OpenMP target regions is not supported yet.
+